The present invention relates to a method for controlling the temperature of an interior, particularly for a motor vehicle, and more particularly, to a method for controlling an interior-temperature with an inner control loop to control the temperature of a medium acting thermally on the interior, and the desired medium temperature is specified as a reference variable for the inner control loop by an outer control loop as a function of an interior-temperature error.
A temperature control method is described in DE 41 23 882 A1 in the form of a heating control system for a motor vehicle interior. Air which is fed to a heat exchanger from outside and then from the heat exchanger is blown into the vehicle interior simultaneously forms the medium in the interior and the medium exerting a thermal action on the interior. An inner control loop adjusts the temperature of the air blown in accordance with a specified desired blow-in air temperature. This desired blow-in air temperature, for its part, is obtained as the manipulated variable of an outer control loop, the reference variable of which is given by the desired interior temperature set by the user. In the case of small interior-temperature deviations, the manipulated variable of the outer control loop is normally determined by means of a PI control facility, the I-component advantageously ensuring the achievement of an infinitesimal deviation. In the case of large deviations, e.g. due to receding disturbances, such as, for example, a falling outside temperature following previous strong irradiation by the sun, however, the PI control facility does not respond as rapidly as desired. The known method therefore envisages to switch over control to purely P control at a specified limiting value in the event of an excessively large deviation of the outer control loop in at least one direction.
For controlling the interior temperature, particularly of a motor vehicle, it is known from DE 36 10 962 C2 that the temperature of the inflowing air can be recorded by an appropriate temperature sensor and weighted as a function of the deviation of the interior temperature.
For temperature control by a mixing-valve thermostat, DE 34 25 445 A1 describes an inner control loop acting as a regulating unit on the mixing valve and an outer control loop arranged on the input side and having a temperature controller. It is possible for the temperature controller to be a PI controller and, with its manipulated variable signal, to produce the reference variable signal for the inner control loop.
Offenlegungsschrift DE 31 21 031 A1 discloses a device for controlling the temperature of a heating boiler which comprises a PI controller and a comparator connected in parallel with the latter. As long as the actual temperature in a heating-up phase remains below a specifiable limiting value which, in turn, is somewhat lower than the specified desired temperature value, the comparator emits an output signal which, on the one hand, keeps the PI controller switched off and, on the other hand, acts as a control signal for heating up. As soon as the actual temperature exceeds the limiting value, the comparator switches over and the PI controller assumes control of the temperature.
An object of the present invention is to provide a temperature controlling method in which errors occurring as control continues can be reliably eliminated and initial relatively large deviations from the control equilibrium can be reduced as rapidly as possible in a starting phase.
This object has been achieved in accordance with the present invention by a method in which
(a) at least one limiting value for starting operation is specified, for a temperature parameter representative of the initial control system state, and at least one switchover limiting value for the interior-temperature error, PA1 (b) at the beginning of each activation of the control system, an actual value of a temperature parameter representative of an initial control system state is compared with a specified limiting value to obtain an error and, if the limiting value has been exceeded, an offset desired temperature of the medium by the outer control loop is determined such that a value of the manipulated variable with a maximum counteractive action is set by the inner control loop until the interior-temperature error assumes a lower-magnitude value than the specified switch-over limiting value for the error, and thereafter continuing control by determination of the desired temperature via PI control, and, if the limiting value has not been exceeded, and PA1 (c) control is immediately carried out by determination of the desired temperature of the medium by a PI control facility.
At least one limit value is specified for starting operation for a temperature parameter representative of the initial control system state, such as, for example, the initial interior-temperature error or the cooling-water temperature of a motor-vehicle heating or air-conditioning system. That specification is used to determine the small amount by which this starting state is allowed to differ from the desired control equilibrium, i.e. from the state when the control system has run in, while still allowing control to be started immediately by the PI control facility.
If, however, the starting state of the control is further away from the control equilibrium then specified by this specified limiting value, control is initially carried out with a maximum counteractive action, in particular by the generation of an appropriate offset desired temperature of the medium by the outer control loop. This offset value acts on the inner control loop such that the latter sets an associated upper value for the manipulating range and hence effects maximum counteractive control. Irrespective of how far the initial temperature-parameter actual value specific to the starting state is from the specified limiting value on the side away from the control equilibrium, the initial control equilibrium is in this way immediately counteracted to the maximum degree until the interior-temperature error exceeds a switchover limiting value, specified for this very purpose, towards small deviations, after which control continues in the PI control mode; and
The method of the present invention thus combines PI control, which is advantageous in control operation after running in, and a starting mode, dependent on the starting state of the control system, in a starting phase. In the case of relatively small initial deviations from the control equilibrium, the starting phase comprises immediate PI control but, in the case of relatively large initial deviations, comprises a preceding control mode with a maximum counteractive action. Thereby, the control equilibrium can be achieved more rapidly than where PI control is used immediately. In particular, it is possible with the method of the present invention to counteract large deviations even more rapidly than is possible with P control.
The method of the present invention furthermore ensures that, by appropriate adjustment of the temperature of the inflowing medium, the interior temperature is always adjusted to the desired interior temperature set irrespective of the respective temperature of the exterior space from which, for example in the case of a vehicle air-conditioning system, the medium for the interior is taken. For this purpose the medium is, if required, cooled and/or heated before flowing in. The use of PI control in the case of small deviations makes it possible to achieve the desired interior temperature accurately without it being absolutely necessary to employ an outside temperature sensor for this purpose.
According to a further aspect of the present invention, the manipulated variable of the outer control loop is fed to the inner control loop with a time delay as a reference variable. Thereby, it is possible to adapt control in a suitable manner to the temperature change behavior with time of the system to be controlled, for example a vehicle interior. Undesirably severe fluctuations in the temperature of the inflowing medium are thus prevented.
Another advantageous feature of the present invention provides that the outer control loop determines the offset desired temperature from the sum of the actual temperature value of the medium and a preselectable time-independent additional temperature value. The latter thus corresponds, apart from any slight modification due to the time-delayed transmission of the signal between the outer and the inner control loop, to the error for the inner control loop and is therefore preselected so that it leads there to the generation of an upper value for the manipulated-variable range that counteracts the deviation to the maximum extent.
In yet another advantageous aspect of the present invention, a starting value for a PI control operation following a starting phase with maximum counteractive control after the corresponding switchover limiting value has been exceeded is specified. In that control operation, the desired temperature value of the medium is calculated continuously by a recursive method from the previous desired value and interior-temperature deviations determined in the preceding steps. The starting value is formed as the sum of the actual temperature value of the medium and a preselectable additional temperature value. This feature makes it possible to specify the preselectable additional value suitably depending on the system so that control with the maximum effect of the manipulated variable merges as continuously as possible into Pi control after the limiting value is exceeded and, in particular, the additional value is preselectable as a function of the outside temperature. As a result, whatever the outside temperature, only an insignificant transient control response occurs in each case.
A still further advantageous feature of the present invention is that, after initial maximum counteractive control by the full heating or cooling capacity available, the PI control facility is in each case activated once the interior-temperature error is sufficiently small in magnitude.
The interior-temperature error is, according to the present invention, used as the temperature parameter representative of the initial control system state. The specified limiting values for starting operation are chosen such that the lower limiting value for starting operation is smaller than each switchover limiting value and the upper limiting value for starting operation is larger than each switchover limiting value.
In an alternative embodiment of the present invention, the cooling-water temperature of a vehicle heating or air-conditioning system is used as the temperature parameter representative of the initial control system state. The initial mode with maximum counteractive control is activated if a specified limiting value for the cooling-water temperature as the limiting value for starting operation is undershot.